Test alcohol concentration with MQ3 and LM3914, MQ3 Alcohol Tester
Keywords: MQ3, LM3914, alcohol concentration test circuit diagram
Author: Li Jian Tao
Hardware circuit design
As shown in the drawings, the front end portion of the circuit can be designed in accordance with a conventional design. The circuit that drives the sound and light indication is performed, and a plurality of illuminated tubes and a buzzer need to be driven, that is, the voltage derived from the voltage divider circuit is required to display the LED line segment, while driving the buzzer at a certain point. Therefore, this design is proposed to display the driving chip LM3914 as an actuator using the LED universal level.
1. MQ-3 gas sensitive sensor
This design uses surface resistance controlled alcohol gas concentration gas sensor MQ-3. The sensitive material of the gas sensor is a highly active metal oxide semiconductor, most commonly used, for example, SNO2. When the surface of the n-type semiconductor, when the reducing gas having a smaller dissociation (volatile electron) at high temperature, the electrons in the gas molecule will transfer to the MQ3 gas-sensitive surface to make the free electron concentration in the gas-sensitive resistance. Increase, the resistivity is reduced, and the resistance is reduced. MQ-3 is applied to a home, factory, a gas leak monitoring device, fireproof and safety detection system. Gas leakage alarm. Gas leak detector. Features: High sensitivity, fast response recovery, excellent stability, long life, drive circuit simple, electrical signal output is strong.
2. The LED universal level display drive chip LM3914 LLM3914 has 10 voltage comparators, and 10 1k ohm precision resistors consisting of a voltage divider providing a comparison benchmark to each voltage comparator, and linearly drives 10 light-emitting diodes (LEDs). 10 paragraph "line" or "point" style chart display; the change in the measured changes are reflected in the rapid truth; no damping phenomenon; strong anti-interference ability. Using 10 light-emitting diodes as a display of input-end levels. The input terminal signal can be a variety of physical quantities detected by various sensors and transform circuits. Such as voltages, current, temperature, humidity, brightness, loudness, audio, distance, magnetic field strength, weight, etc. With the level display it made, it is awake, intuitive, and convenient, practical, and can reflect the instantaneous changes. The use is very widespread. For example, in the circuit design and production. It can achieve temperature control and display through probes and processing circuits. Used in ovens, refrigerators, air conditioners, thermoplasts, etc., can also achieve intuitive display of high voltage by the voltage conversion circuit. For instruments, meters, audio and office equipment. The core circuit uses a flood-seal double-column-in-in-in-in-in-line display drive integrated circuit LM3914. The LM3914 contains 10 identical voltage comparators, which can directly drive the external 10 light-emitting diode (VD1-VD10) as a strip display, or point-like display. At this point, their inverting inputs are connected in parallel. And connect to the input 5 feet through a buffer. The 10 co-phase inputs are connected to a multi-stage voltage divider formed by 10 precision resistors. The inside of this divider is not connected to other circuits or the common end, but is directly from 6, 4 foots, usually referred to as a suspension. This makes the design of the application circuit more flexible and convenient.
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The following is an example of a 10-level linear voltmeter having a resolution of 0.125V, and the working principle is explained. The maximum speed of this voltage meter is 1.25V, which is connected, (11), set to point-like display, which is more power saving. The voltage divider is connected to the internal reference voltage source, 6, 7 foot, 4 foots. The pressure drop on each 1K resistor is 0.125 V, so the potential of the athlete input end is 0.125 V, and the comparator 2 is 0.25V. So on and so forth. The topmost comparator 10 is set to 1.25V. When the 5 foot input voltage is less than 0.125V, 10 LEDs do not illuminate. When the input voltage is greater than 0.125V but less than 0.25V. The comparator 1 inverted input power is higher than the same phase input, the comparator 1 outputs a low potential, so that the VD1 is emitted; when the input voltage is greater than 0.25V, the VD2 is emitted; according to such push, when entering 1.25V VD10 illuminates the voltage. The above is the use of 10 LEDs 0-1.25V ten, 0.125V per level; if the 6 foot is external 10V standard voltage source, 4 foots. It can be 0-10V ten-level voltmeter, if 6 foot is 10V, 4 foots 5V voltage. Then, a voltage meter of 5-10V is displayed, 0.5V per stage. But should pay attention to the 6 foot voltages at least 2V at least 2V.
3. Circuit work principle
This design uses 5V power supply, the front end is the MQ-3 alcohol gas concentration sensor. With the resistance division circuit, the aluminum concentration is converted to a voltage amount, and then the corresponding luminescence pipe is driven by the driving chip LM3914, and the buzzer is triggered when the set threshold is reached, and the alarm is sent. The measurement sensitivity is adjusted by the potentiometer RP when debugging.
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